This invention relates to a welding torch for use in gas metal arc welding.
Welding torches for use in gas metal arc welding are well known. The gas metal arc welding is often referred to as MIG (metal inert gas) welding. The welding process uses an electrical arc between a consumable electrode wire and a weld being formed. The weld being formed is protected from atmospheric contamination by a blanket of shielding gas which is an inert gas, or a combination of an inert gas plus other gases.
The known welding torches comprise a neck portion, a diffuser at a first end of the neck portion, a contact tip which extends from the diffuser, and connector means which is at a second end of the neck portion and which is for connecting the neck portion to a power cable assembly. The neck portion comprises an electrical conductor and a longitudinally extending passageway. The power cable assembly is such that it supplies electricity and gas to the welding torch. The welding torch causes the gas from the power cable assembly to flow along the passageway and out of the welding torch through at least one aperture in the diffuser. The gas is usually supplied without the application of pressure.
The neck portion of the welding torch is often referred to as a swan neck or a goose neck. The consumable electrode wire passes continuously through the diffuser and is consumed during the welding. The contact tip transfers the electric current from the electrical conductor in the neck portion to the continuously moving consumable electrode wire.
The consumable electrode wire is consumed at a relatively high speed. Electrical current transfer efficiency from the electrical conductor in the neck portion to the diffuser and the contact tip is of paramount importance. Heat generated in the current transfer and in the proximity of the arc directly affects the efficiency of the contact tip. The contact tip is made of copper or a copper alloy because of the need to use a material which has good electrical conductivity. However, the copper or the copper alloy is prone to expand and self-anneal. The contact tip material thus becomes soft, which in turn gives a decreased wear resistance, and also impinges on free movement between a bore in the contact tip and the consumable electrode wire which passes through this bore.
It is an aim of the present invention to reduce the above mentioned problems by providing a welding torch which has improved contact tip electrical current transfer, and which utilizes the gas used for shielding the weld also as a cooling agent for cooling a substantial part of the contact tip surface area.
Accordingly, in one non-limiting embodiment of the present invention there is provided a welding torch for use in gas metal arc welding, which welding torch comprises a neck portion, a diffuser at a first end of the neck portion, a contact tip which extends from the diffuser, and connector means which is at a second end of the neck portion and which is for connecting the neck portion to a power cable assembly: the neck portion being such that it comprises an electrical conductor and a longitudinally extending passageway; the power cable assembly being such that it supplies electricity and gas to the welding torch, the gas being for protecting welds from atmospheric contamination as the welds are made using the welding torch; the welding torch being such that it causes the gas from the power cable assembly to flow along the longitudinally extending passageway and out of the welding torch through at least one aperture in the diffuser; the welding torch being such that the electrical current transfer from the electrical conductor to the contact tip is effected using first and second longitudinally separated contact areas on the contact tip, the first contact area being an end face of the contact tip adjacent the diffuser, and the second contact area being a threaded portion of the contact tip which secures the contact tip in the diffuser; and the welding torch being such that it includes a gas chamber which is positioned longitudinally between the two contact areas and radially between the contact tip and the diffuser whereby the gas in the gas chamber flows over a part of the contact tip between the two contact areas and cools this part of the contact tip before flowing out of the welding torch through the said at least one aperture in the diffuser.
The welding torch of the present invention is thus able to provide good metal to metal contact at the two contact areas. The welding torch is also able to use the gas in an extra capacity for the cooling of the part of the contact tip. The efficiency of operation of the welding torch of the present invention is thus increased over the above mentioned known welding torches.
Preferably, the welding torch is one in which the end face of the contact tip abuts against a transverse face of an internal part of the diffuser. The conductor then abuts against an opposite side of this internal part of the diffuser. Alternative arrangements may be employed so that, for example, the end face of the contact tip may be arranged to abut directly against an end face of the conductor.
As mentioned above, the MIG welding utilizes a consumable electrode wire. This consumable electrode wire is commonly referred to as the welding wire and it is continuously fed through a guide tube known as a wire liner. The wire liner is situated within a central core tube of the power cable assembly. The gas passes along the length of the welding torch, from where it is directed over a weld being formed. Such known welding torches are basically air cooled and they normally use only the surrounding ambient air temperature to dissipate heat that builds up within the welding torch. The welding torches are thus given working duty cycles. Currently, the normal European duty cycle is 60% of a 5-minute cycle, that is 3 minutes of welding followed by two minutes of rest.
Accordingly to one embodiment of the present invention, the electrical conductor comprises an inner tube and an outer tube which is positioned over the inner tube, and the longitudinally extending passageway is positioned between the inner and outer tubes. With such an arrangement improved cooling may be achieved as compared with known welding torches. More specifically, the welding torch of the present invention will usually be air cooled, but it may be water cooled if desired. The gas is able to perform a cooling function, in addition to its function of shielding the weld being formed from atmospheric contamination. The cooling effect of the gas makes the welding torch more efficient than it would otherwise be. For example, in the case of an air cooled welding torch, the torch of the present invention is able to operate at a duty cycle of 80% as compared to the above mentioned normal duty cycle of 60%. The invention is based on the observation that the gas flow through normal welding torches is a simple and straight direct flow line, which has very little cooling effect since the gas used is only used for one purpose, which is to avoid atmospheric contamination of the weld being formed. By redirecting the gas flow, the gas can have an important second purpose, namely providing a cooling function to the welding torch.
Preferably, the welding torch is one in which the inner tube has a fluted outer profile, in which the outer tube is positioned over the fluted outer profile of the inner tube, and in which the longitudinally extending passageway is formed by spaces between the flutes. Other arrangements may be employed if desired so that, for example, the inner tube could be plain whilst the outer tube had inwardly directed flutes. Alternatively, the flutes could be screw threads.
The welding torch may have an axial central passageway which is blocked so that the gas cannot pass along the axial central passageway and is caused to be redirected along a heat cooling path through the welding torch. This is preferably effected by the welding torch being one which has metal to metal contact between the contact tip and the diffuser and between the diffuser and the electrical conductor, the metal to metal contact being such as to block axial central passageway and to redirect the flow of gas from the power cable assembly through the welding torch such that the redirected gas flows along the passageway between the inner and outer tubes of the neck portion and out of the welding torch through the aperture in the diffuser.
The welding torch may be one in which the neck portion comprises a first chamber which communicates with an upstream end of the electrical conductor and which receives the gas before it passes between the inner and outer tubes of the electrical conductor, in which the diffuser comprises a second chamber which communicates with a downstream end of the electrical conductor and which receives the gas from the inner and outer tubes of the electrical conductor, and in which the diffuser comprises a third chamber which causes the gas from the second chamber to flow over the contact tip before the gas leaves the welding torch.